An in-memory database system is a database system that primarily uses main memory for data storage. One example of an in-memory database system is the HANA in-memory database system provided by SAP AG of Walldorf Germany. As opposed to employing a disk storage mechanism for storing business data, in-memory database systems such as HANA use main memory, which is faster than disk-based databases since disk access and retrieval functions involve moving mechanical parts, which makes it much slower than main memory access. Accessing data in main memory reduces the input/output reading activity when querying the data, which in turn provides faster and more predictable performance than disk.
However, there are some scenarios where storing data to an in-memory database is not optimal. For example, a large object (LOB) can consume a large amount of memory space, and while the cost of in-memory solutions is continually decreasing, the storage and processing of some LOBs may slow down overall performance of the in-memory database system. For LOBs that consist of a number of megabytes or even gigabytes of data, storing LOBs to main memory is not appropriate since it might waste a lot of main memory. Therefore there is a need to ascertain when and under which parameters such LOB data is to be stored on disk.